The present invention relates to lubricants for manual transmissions with improved performance with sintered synchromesh components. Problems occur with synchromesh parts in a manual transmission with many oils having too low friction or high wear of the components leading to synchromesh damage and poor or failed gear shifts.
The synchronizer is one of the more important components of any manual gearbox. Increasing performance, reducing shift force and minimizing the between-the-gears energy losses are the primary objectives for a new generation of synchronizer systems. Improvements in the capacity of the brass system and the introduction of formed sintered cones are allowing economical re-engineering of existing synchronizer designs into more efficient designs (see Hoerbiger and Co. Engineering Report 32). The chemistry of manual transmission lubricating oils needs to be reformulated for these designs to be able to maintain adequate friction between the sintered cones and protect these parts from wear.
Conventional gear oils or manual transmission oils typically contain chemical components, such as active sulfur and surface-active amine organophosphates. While excellent as additives to provide extreme pressure lubrication, in the usual amounts these additives alone are too slippery and do not adequately protect the sintered surfaces from abrasive or corrosive wear.
Poat et al. in U.S. Pat. No. 5,691,283 disclose a method of operating a vehicle having a manual transmission with a cone synchronizer using fluids with improved friction characteristics containing mineral or synthetic oils, one or more Mannich dispersants including borated Mannich dispersants, metal free sulfur containing antiwear and/or extreme pressure agents, one or more phosphorus containing and nitrogen containing antiwear and/or extreme pressure agents, and overbased alkali metal or alkaline earth metal detergents. The method may employ a finished lubricant in which all or a portion of the base oil is a polyalphaolefin (PAO). Other potential additives are listed including Cu corrosion inhibitors, which may be synonymous with xe2x80x9cmetal deactivators.xe2x80x9d No specific ones are named. There is no mention of a synchronizer with sintered metal parts but instead the emphasis is on steel units with molybdenum-based plasma spray coatings. Poat et al. in EP 0 767 236 disclose improving the frictional characteristics of manual transmissions of the synchronizer type with compositions of more than 40% hydrogenated poly-a-olefins and 0.01-2% of an overbased alkaline earth metal sulfurized phenate or salicylate. Additive packages are described as generally containing a sulfur-phosphorus antiwear or extreme-pressure additive system, one or more antioxidants, one or more corrosion inhibitors and an antifoam additive and may, preferably contain a dispersant additive. There is no mention of a specific metal deactivator, and there is no mention of sintered metal parts.
Wallace et al., in U.S. Pat. No. 5,492,638, disclose a method similar to the Poat et al. patent, disclosing the same list of required components but as a method of improving gear shift performance.
Schwind et al. in U.S. Pat. No. 4,792,410 disclose the synchromesh manual transmission fluids. A composition is disclosed in Example IV for a manual transmission fluid containing a mixture of synthetic materials including a majority of PAO as the base stock, a zinc dithiophosphate and dioleylphoshite as extreme pressure (EP)/antiwear agents, a sulfurized olefin EP agent, a magnesium sulfonate detergent, and a borated carbonate overbased sodium sulfonate. Schwind et al. in WO 87/05927 disclose similar examples and claims alkaline earth metal detergents with synthetic oils for manual transmission fluids. No metal deactivators or amine phosphates are disclosed in either and the only boron is in the form of the borated detergent not a borated dispersant. Synchromesh with sintered parts is not disclosed.
Teqjui et al. in EP 0976813 disclose high synchromesh durability performance and gear protection of a manual transmission gearbox. Metal detergents are presented as a required component as overbased salicylates and a calcium sulfonate is shown in the comparative examples. Metal deactivators are described as optional components at up to 7%, with specific mention of up to 3.5% of a dimercaptothiadiazole derivative. The patent discloses specific metal borate containing formulations for manual transmission fluids. The synchromesh durability testing shown involves brass or Mo/steel synchronizers, not sintered metal. No synthetic oil is disclosed.
Shubken et al. in U.S. Pat. No. 4,172,855 disclose a process for manufacturing alpha olefin oligomers useful as synthetic lubricant base oils. Example 2 shows the combination of the PAO with a calcium sulfonate with other additives in an engine crankcase lubricant.
Similarly, Howie et al. in U.S. Pat. No. 4,525,289 in Example IIC disclose a formulation that has a PAO in combination with a overbased calcium sulfonate and an overbased magnesium sulfonate as a crankcase lubricant.
In a paper by O""Connor et al., entitled Axle Efficiency Response to Synthetic Lubricant Components (SAE Paper No. 821181), presented at the Fuels and Lubricants Meeting in Toronto, Ontario, Canada, in October 1982) the authors state that xe2x80x9cinvestigations with both partial- and full-synthetic base formulations have shown improvements compared to conventional petroleum based gear oils. Maximum benefits are gained with total synthetic base type formulations.xe2x80x9d This paper teaches the value of synthetic oils for axle efficiency that would result in fuel savings. The chemistry is not disclosed. The paper mentions that there is a 50% over-treatment of the EP additive to insure GL-5 quality, the gear oil performance standard, and that all EP additives used were commercial SP types. (This would typically mean sulfur(S) as sulfurized olefins and phosphorous(P) as amine phosphates.) There is no disclosure that basic metal detergents would also be present and there is no discussion of manual transmissions, or synchromesh manual transmissions, or the latter with sintered metal parts.
All of the above prior art references reveal the use of the various components in lubricants in some capacity and even some combinations in manual transmissions. None of the references teach the specified combinations of this invention or the advantages of these combinations in manual transmission fluids with sintered metal synchronizers. None of the references address the problems of wear or low friction of fluids in synchromesh manual transmissions with sintered metal parts.
The present invention solves the problem of wear and too low friction in a manual transmission with sintered metal parts in the synchronizer of the transmission by using a lubricating oil formulated with a high level of an alkaline earth sulfonate in combination with amine phosphates.
The present invention provides a composition suitable for lubricating a manual transmission designed with sintered metal surfaces in the synchronizer, comprising:
(a) at least about 70% by weight of oil of lubricating viscosity of API Group III, IV, V or mixtures thereof,
(b) about 0.01 to about 2% by weight of an amine salt of a phosphorus containing acid,
(c) at least about 0.5% by weight of a basic metal salt of an organic acid,
(d) about 0% to about 0.7% by weight of a metal deactivator compound, and
(e) about 0% to about 3% by weight of a boron-containing dispersant.
The present invention further provides a method for preventing wear of sintered metal surfaces in the synchronizer of a manual transmission and improving performance by using a lubricant of the composition of the present invention. The lubricating composition is characterized by the selection of a stable base oil and high levels of metal detergents, an amine phosphate extreme-pressure agent and other gear oil additives. The method further enhances performance with the addition of either or both of the metal deactivator compound and/or the boron-containing dispersant to the lubricating composition.
Various preferred features and embodiments will be described below by way of non-limiting illustration.
Component (a) of the lubricating composition is an oil of lubricating viscosity of API Group III, IV or V. Specific examples of this type of component include but are not limited to severely hydrogenated mineral oils (Group III), polyalpha-olefins (PAOs) (Group IV) or other synthetics (Group V) such as alkyl benzenes.
The amount of component (a) in the compositions of the present invention is generally in the range of about 70% to about 96% by weight of the lubricating composition. Preferably the amount of component (a) is in the range of about 80% to about 95% by weight of the lubricating composition. More preferably the amount of component (a) is in the range of about 85% to about 93% by weight of the lubricating composition.
Preferably component (a) is a Group III or Group IV oil or mixture of both. Preferably component (a) comprises about at least 35% by weight PAO, more preferably about at least 50% by weight PAO, and most preferably about at least 70% by weight PAO.
Component (b) of the lubricating composition is an amine salt of a phosphorus-containing acid. Specific examples of this type of component include but are not limited to amine salts of partial esters of phosphoric or thiophosphoric acids.
In one embodiment, the phosphorus-containing acid is a phosphorus acid ester prepared by reacting one or more phosphorus acid or anhydride with an alcohol containing from one to about 3 carbon atoms. The alcohol generally contains up to about 30, preferably up to about 24, and more preferably up to about 12 carbon atoms. The phosphorus acid or anhydride is generally an inorganic phosphorus reagent, such as phosphorus pentoxide, phosphorus trioxide, phosphorus tetroxide, phosphorus acid, phosphorus halide, lower phosphorus esters, or a phosphorus sulfide, including phosphorus pentasulfide, and the like. Examples of phosphorus acids or anhydrides include phosphorus pentoxide, phosphorus pentasulfide and phosphorus trichloride. Lower phosphorus acid esters generally contain from 1 to about 7 carbon atoms in each ester group. The phosphorus acid ester may be a mono- or diphosphoric acid esters. Alcohols used to prepare the phosphorus acid esters include but are not limited to butyl, amyl, 2-ethylhexyl, hexyl, octyl, decyl and oleyl alcohols and the like. Examples of commercially available alcohols include Alfol 810 (a mixture of primarily straight chain, primary alcohols having from 8 to 10 carbon atoms); Alfol 1218 (a mixture of synthetic, primary, straight-chain alcohols containing 12 to 18 carbon atoms); Alfol 20+ alcohols (mixtures of C18-C28 primary alcohols having mostly C20 alcohols as determined by GLC (gas-liquid-chromatography)); and Alfol 22+ alcohols (C18-C28 primary alcohols containing primarily C22 alcohols). Alfol alcohols are available from Conoco.
Other examples of commercially available alcohol mixtures are Adol 60 (about 75% by weight of a straight chain C22 primary alcohol, about 15% of a C20 primary alcohol and about 8% of C18 and C24 alcohols) and Adol 320 (oleyl alcohol). The Adol alcohols are available from Ashland Chemical.
A variety of mixtures of monohydric fatty alcohols derived from naturally occurring triglycerides and ranging in chain length of from about C8 to C18 are available from Procter and Gamble Company. These mixtures contain various amounts of fatty alcohols containing mainly 12, 14, 16, or 18 carbon atoms. For example, CO-1214 is a fatty alcohol mixture containing 0.5% of C10 alcohol, 66.0% of C12 alcohol, 26.0% of C14 alcohol and 6.5% of C16 alcohol.
Another group of commercially available mixtures include the xe2x80x9cNeodolxe2x80x9d products available from Shell Chemical Co. For example, Neodol 23 is a mixture of C12 and C13 alcohols; Neodol 25 is a mixture of C12 to C15 alcohols; and Neodol 45 is a mixture of C14 to C15 linear alcohols. Neodol 91 is a mixture of C9, C10 and C11 alcohols.
Fatty vicinal diols also are useful and these include those available from Ashland Oil under the general trade designation Adol 114 and Adol 158. The former is derived from a straight chain alpha olefin fraction of C11-C14, and the latter is derived from a C15-C18 fraction.
In another embodiment, the phosphorus-containing acid is a thiophosphorus acid ester. The thiophosphorus acid esters may be mono- or dithiophosphorus acid esters. Thiophosphorus acid esters are also referred to generally as thiophosphoric acids. The thiophosphorus acid ester may be prepared by reacting a phosphorus sulfide, such as those described above, with an alcohol, such as those described above.
In one embodiment, the phosphorus acid ester is a monothiophosphoric acid ester or a monothiophosphate. Monothiophosphates may be prepared by the reaction of a sulfur source with a dihydrocarbyl phosphite. The sulfur source may for instance be elemental sulfur. The sulfur source may also be an organosufide, such as a sulfur coupled olefin or a sulfur coupled dithiophosphate. Elemental sulfur is a preferred sulfur source. The preparation of monothiophosphates is disclosed in U.S. Pat. No. 4,755,311 and PCT Publication WO 87/07638, incorporated herein by reference for their disclosure of monothiophosphates, sulfur sources, and the process for making monothiophosphates. Monothiophosphates may also be formed in the lubricant blend by adding a dihydrocarbyl phosphite to a lubricating composition containing a sulfur source, such as a sulfurized olefin. The phosphite may-react with the sulfur source under blending conditions (i.e., temperatures from about 30xc2x0 C. to about 100xc2x0 C. or higher) to form the monothiophosphate salt with an amine which is present in the blend.
In another embodiment, the phosphorus-containing acid is a dithiophosphoric acid or phosphorodithioic acid. The dithiophosphoric acid may be represented by the formula (RO)2PSSH wherein each R is independently a hydrocarbyl group containing from about 3 to about 30 carbon atoms. R generally contains up to about 18, preferably to about 12, and more preferably to about 8 carbon atoms. Examples of R include but are not limited to isopropyl, isobutyl, n-butyl, sec-butyl, the various amyl, n-hexyl, methylisobutyl carbinyl, heptyl, 2-ethylhexyl, isooctyl, nonyl, behenyl, decyl, dodecyl, tridecyl groups and the like. Illustrative lower alkylphenyl R groups include butylphenyl, amylphenyl, heptylphenyl and the like. Examples of mixtures of R groups include, but are not limited to 1-butyl and 1-octyl; 1-pentyl and 2-ethyl-1-hexyl; isobutyl and n-hexyl; isobutyl and isoamyl; 2-propyl and 2-methyl-4-pentyl; isopropyl and sec-butyl; and isopropyl, isooctyl and the like.
In one embodiment, the dithiophosphoric acid may be reacted with an epoxide or a glycol. This reaction product is further reacted with a phosphorus acid, anhydride, or lower ester. The epoxide is generally an aliphatic epoxide or a styrene oxide. Examples of useful epoxides include ethylene oxide, propylene oxide, butene oxide, octene oxide, dodecene oxide, styrene oxide and the like. Propylene oxide is preferred. The glycols may be aliphatic glycols having from 1 to 12, preferably 2 to 6, and more preferably 2 or 3 carbon atoms. The dithiophosphoric acids, glycols, epoxides, inorganic phosphorus reagents and methods of reacting the same are described in U.S. Pat. Nos. 3,197,405 and 3,544,465, incorporated herein by reference for their disclosure to these.